I'm a firm believer of Hanlon's Razor, but over a week, Facebook has flagged a post and a comment of mine, both about Mastodon (and including a link to joinmastodon.org)
🤔🤔🤔🤔🤔🤔
@yhancik Before I was banned by Twitter (their AI thought I was a conspiracy theorist for making fun of them), I also had the impression that Tweets linking to joinmastodon.org did less well than expected. So I mostly linked to a blog post of mine, which linked to joinmastodon.org.
If true that would be anti-competitive behavior, which is officially illegal. I find it hard to believe they would risk that. If someone sings that can cost them a lot of money.
Facebook and Youtube actively discourage external links (to anything) in posts/comments, there are also settings on YT where the channel owner can choose whether or not to allow external links (not sure whether FB allows community mods to decide this or applies its own automatic policies as I've never used it). I noticed this when trying to comment on YouTube with a link to the Dutch public news service; in this case the comment simply disappeared without any warning >>
I suspect the corporate social networks aren't singling out Mastodon as such, but discouraging *any* site that could lead the discussion elsewhere (as they are losing out on traffic and potential viewers of ads), a link to an old style forum about pets, cars, electronics would be quite likely to also trigger this (even on those forums if you make lots of links in your first few posts they are usually flagged up for the moderators to check)
@vfrmedia @VictorVenema @yhancik I had 2 YT comments in a row disappear without warning or feedback a few weeks ago and each contained links to different external sites (one to a well known credible blog, another to a peertube instance). Didn't know why...thought I got banned in some way but then a later comment stuck.
I guess the mystery is solved 
I guess the silos are catching on to the POSSE strategy (Publish Own Site, Syndicate Elsewhere) and trying to suppress it, but in my opinion that is anti-competitive behaviour and any antitrust decrees should ban the Silos from doing this (only malicious links found through human moderation or user reports should be acted upon)
@vfrmedia @VictorVenema @yhancik the Social Silos and their algorithms have fostered a culture of extreme and sometimes illogical suspicion as well.
From May of 2017 when I set up my masto server until Jan 1 2018 when I deleted my Facebook account all my posts were links to my posts on coales.co (my first real attempt at POSSE). FB didn't seem to remove or overtly suppress them but engagement went WAY down, and literally about half the responses I got were DMs from friends saying something like "hey I'm getting all these posts from you linking to this weird coales.co site I think you have a virus"
*sigh*
So I resolved to quit FB for 2018 and have enjoyed the #BOMO (bliss of missing out) ever since.
@vfrmedia @msh @VictorVenema and there's Instagram simply not supporting any link, giving us the cursed "link in bio" thing.
I think there's definitely a certain hostility toward hypertext in their algos, and I suspect there is valid concerns for spam & malware, meeting their own interests in keeping people on their app.
Spam is actually the argument used by Pixelfed for copying the anti-link approach of Instagram. And I was just thinking the other day... spam really does ruin a lot of things
@vfrmedia @msh @VictorVenema it's an irrelevant anecdote, but I noticed last week that the newsletter of the non-profit where I work gets a high amount of hard bounces from mail providers whenever I've used an harmless unicode character in the subject. And of course, that's all because spammers have been abusing unicode characters to, among other things, circumvent spam filters.
@msh @VictorVenema @yhancik
there's also marketing tactics of startup social networks (including LinkedIn at one point) where they try and email all of your contacts to get them to join..
there may be is a case to use legislation against this, but it will vary between countries and there would need to be proof found that GAFAM are colluding to only share links amongst themselves (YT links on Facebook groups seem to get through) and its not local moderators leaving default setting active..